Sound reproducer



March. 10, 1931. DE R T 1,795,936

, SOUND REPRODUQER Filed Sept. 11, 1926 ea De fireJs/ Patented Mar. 10, 1931 UNITED STATES PATENT OFFICE In atom, 01' YORK, IN. YL, ASSIGNOB, BY IESI IE ASSIGNMENTS, '1'0 GENERAL TALKING PIGL'UBES COBIOBATION', A OORIORA'I'ION OI DELAWARE SOUND REPRODUGEB Application filed September 11, 1926. Ierlal ll'o. 184,781.

This invention relates broadly to improved.

sound reproducing combination One the provision of a suitable form of sound 5 reproducing device for use in conjunction; with motion picture screens in auditoriumfs."

Another object of this invention is to pro duce a combination in which the loud speaker is so arranged with respectto the motion picture screen that the sounds issuing therefrom will appear to emanate from the screen.

A still further object ofthis invention is to so combine the loud speaking device with the screen structure that they may be moved 16 conjointly out of their normal position when it is desired to utilize the stage for other purposes.

A still further object of this invention is to so arrange the aperture of the loud speak- 20 inlg device so that its major axis is horizon- A still further object of the invention is the disposition of a loud speaking device of relatively long dimensions, whose major axis is parallel to the plane of the screen.

These-and many other objects are successfully sought b my invention, as will appear from the ollowing description.

This invention resides substantially in the combination, construction, arrangement and relative location of parts, as will appear in the following disclosure.

Referring to the drawings- Fig. 1 represents a front elevational view of, a motion picture screen supporting a loud ipeaking unit particularly devised therefor me. Fig. 2 represents a side elevational view ofthis construction, and

Fig. 3 represents. a vertical cross-sectional view of the arrangement of Fig. 1, taken on the line 3--3 of Fig. 1, looking in the direction of the arrows.

Heretofore when talkin have been presented in motion pictures e theatre, 1t. has

eitherone horn located on thestage the ob ects of this invention is oc 'highlydesirable from the standpoint of ilbeen. customary to use for loud eakers irectly beneath the screen, or two,one ated on either side of the screen. The ordinary motion picture screen is of canvas or rubber and -much too thick to permit the loud speaker horn to be placed back of the screen and the sound-waves to permeate through the screen itself. At the same time, it is ts lusion that the loud speaker horns be as near as possible to the screen so that the observers in the audience hearing the sound emanating from some source and watching the figure on the screen will. instinctively think that the sound emanates from the lips of the speaker or from the musical instruments depicted on the screen.

Such horns as I have described are bulky; and frequently it is impracticahfrom the standpoint of stage requirements to,have these horns so located below the screen or on either side thereof. A practical arrange ment requires that the horn should be in fact an integral portion of the screen framework, and itself always. in place relative to this screen even when the screen, as is frequently. the case, must be suddenly lifted from its position in view of the audience to an elevated osition alon the flies above the stage, in order to c ear the stage quickl for presentation of acts, etc., thereon. All of the above considerations render the ordinary form of loud speaker horn quite unsuited for use in the average motion picture house where the screen must be frequently elevated and lowered, and where only small I space is permissible between the screen and the upper flies, or between the screen and the back wall of the stage.

Moreover, I have found that for satisfac- 7 tory realism in talkin motion pictures a very large horn is high y desirable or essential. A horn for a low cut-ofi' value, that is, one capable of faithfully reproducing for-supporting the screen 2 in any of the desired and well known manners. Supported on the screen framework'is a loud speaking horn 3, having its aperture disposed at the top of the screen framework and parallel to the plane thereof. At the small end of the horn is provided any suitable sound reproducing unit 4, which, in the arrangement shown, is supplied by actuating electric currents through the cable 5.

It will be noted that the horn portion of' the sound reproducing device is very long with respect to its cross-sectional dimensions, and is of constantly increasing cross-sectional area from the smaller'end towards the aperture end. The aperture of the horn is preferably made short in a vertical direction and long in a-horizontal direction, and projects above the upper edge of the framework on which the screen is stretched. The mouth of the horn lies in a horizontal plane parallel to that of the screen, but the axis of the main part of the horn itself runs vertically, close to the screen and directly behind same, as is clearly shown in the figures. By such an arrangement I am enabled to secure a great length of horn-as much as twenty (20) feet for the larger theatres (where the greatest volume of sound output is required) combined with a depth of horn not necessarily exceeding twelve (12), or eighteen (18) inches. At the same time the mouth of the horn being long horizontally, for example 48 inches, and short vertically, e. g. 18 inches, gives a very excellent diffusion of sound throughout the amphitheatre, particularly in the vertical plane, so that the sound waves reach all parts of the auditorium, from the front orchestra seats almost directly below the screen to the upper regions of the balconies. For it is a well known law of acoustics that sound difraction results in a diffusion of the sound in planes at right-angles to the long axis of a rectangular opening of a horn rather than in planes parallel to said long axis.

The construction of a horn such as I have described lends itself very easily to the theoretically correct shape for hornsi. e. following the logarithmic or exponential law. This law is briefly expressed as follows:

A =A e Whereinin A is'the cross-sectional area of the horn at the small end. AZ is the cross-sectional area of the horn'at any point along its major axis X and B is a constant determined by the overall length of the horn and the two terminal areas thereof. The cut-off frequency of such a horn is second, and B is the parameter of the-horn. This cut-off frequency for such a horn as above described, having an overall length of eleven (11) feet measured along its center axis and an opening of 48" X18, is of the order of 80; that is, such a horn will reproduce clearly sound frequencies as low as 80 per second. Such an exponential born as I have described has no resonant frequency, andreproduces with practically equal volume all sound frequencies above its lower cut-off level.

Moreover an exponential horn can be made with much smaller dimensions than any other shape of horn giving equal performance. It is for example much superior to the conical type of horn.

Although I can reverse the position of the horn relative to the screen as shown in Fig ure 1that is have its aperture appear at the bottom of the screen, rather than at its top-I have found that both the acoustical effects and the illusion are better when the horns large aperture is located above the screen, as shown. e

Instead of one horn located in the middle of the screen as shown in Figure 1, I may use two or more placed behind the screen, their apertures projecting above the top of the screen. Or I may place these two horns horizontally, behind the screen, and have the apertures thereof appearing at the two lateral margins of the screen. But in every case the horn or horns are referably fastened bodily to the screen, an are made an integral part of the screen structure, so

that they travel with the screen when the same is raised or lowered.

I, of course, intend it to be within the scope of my invention to utilize more than one loud speaking device, when desirable, and to dispose them upon the supporting framework in any effective manner; for instance, several of them may be disposed along the upper surface, if desired.

I am aware that many changes in the details of construction and relative arrangement of parts will readily occur to those skilled in the art, and I do not, therefore, desire to be limited to the particular construction disclosed for purposes of illustration, but rather to my invention as I define it in the appended claim.

tesnmony whereof 1 have hereunto set my on this 31st clay of August, A" 1), 1:32 60 DE FQRESTQ 

